Germany winning WWII is actually fairly easy and straight forward, so I don't understand why it's often considered so impossible. I personally lay the blame on YouTube amateur historians,
who the actual historians have been butting up against in recent years for the former's bad takes. The central question of the "how" is defined by the status of the USSR in the conflict. Mark Stoler's
Allies and Adversaries: The Joint Chiefs of Staff, the Grand Alliance, and U.S. Strategy in World War II reveals the broader planning of the JCS as it concerns the war and situational contingencies therein. From Page 72:
Eisenhower and his subordinates were far from alone or original in perceiving the overriding importance of continued Soviet participation in the war. As previously noted, in the summer and fall of 1941 Roosevelt and army planners had begun to recognize that victory over Germany might not be possible unless the Red Army continued to tie down the bulk of the Wehrmacht, and they consequently had made assistance to Russia a focal point of their global strategy. The JB had forcefully reiterated this conclusion by informing Roosevelt on December 21 that ‘‘Russia alone possesses the manpower potentially able to defeat Germany in Europe.’’ 26 The Soviets’ late 1941 success in stopping the German advance on Moscow and launching a counteroffensive, occurring at a time when Axis forces were everywhere else successful, further reinforced this belief. As a result virtually all Allied planning papers in late 1941– early 1942 stressed the critical importance of aiding the Russians so that they could survive a renewed German onslaught. Roosevelt agreed. ‘‘Nothing would be worse than to have the Russians collapse,’’ he told Treasury secretary Henry Morgenthau on March 11. ‘‘I would rather lose New Zealand, Australia, or anything else than have the Russians collapse.’’ Five days earlier the JUSSC had bluntly stated that ‘‘Russia must be supported now by every possible means’’ because the absence of a Russian front would postpone ‘‘indefinitely’’ the end of the war.27 And as army planners realized, such postponement would only increase public and naval pressure to turn away completely from the indecisive European theater in favor of the Pacific.
Page 80:
Marshall’s reasoning was based not only on Eisenhower’s February–March presentations but also on military and political events since then which had heavily reinforced the OPD’s original conclusions. Once again the focal point was the Soviet Union. ‘‘The retention of Russia in the war as an active participant is vital to Allied victory,’’ now acting chief of staff McNarney had emphasized on April 12; if German armies were allowed to turn west, ‘‘any opportunity for a successful offensive against the European Axis would be virtually eliminated.’’ 56 In mid June the staff again warned that Russian collapse would necessitate a strategic reassessment, ‘‘possibly with the result of directing our main effort to the Pacific rather than the Atlantic.’’ 57
Page 93:
As early as April–May, OPD, g-2, and the joint committees had begun to explore the appropriate response should this ‘‘desperate situation’’ result in a Soviet collapse, and in early August the JUSSC completed and forwarded to the JPS a massive study of such a contingency. This study indicated that Russian collapse would be a ‘‘catastrophe’’ of such magnitude as to put the United States in a ‘‘desperate’’ situation too, one in which it ‘‘would be forced to consider courses of action which would primarily benefit the United States rather than the United Nations.’’
Indeed, it might be the only remaining major member of the United Nations, because the British Commonwealth might collapse and the British public react to Soviet defeat by overthrowing Churchill and agreeing to a negotiated peace that would leave Hitler in control of Eurasia. A revival of isolationism and an ‘‘increase in defeatism’’ within the country were also possible in this scenario. Even without British withdrawal, however, the only sound U.S. response to a Soviet collapse would be to ‘‘adopt the strategic defensive in the European Theater of War and to conduct the strategic offensive in the Japanese theater.’’ On August 19 the JPS the great strategic debate 93 approved this report, forwarded it to the Joint Chiefs as JCS 85, and ordered the preparation of a strategic plan for the defeat of Japan.40
Concurrent to these concerns, the following documents were prepared:
"Conditions under Which an Armistice Might Be Negotiated between the United Nations and the European Powers", on June 11, 1942 by Maj. Gen. George V. Strong (S Document 22)
Col. Nevins, ‘‘Courses of Action Open to the United States in the Event the Prospective 1942 German Offensive Forces Russia to Capitulate,’’ memo, Apr. 1942, and unsigned memo to Nevins, Apr. 25, 1942, Wedemeyer Papers, box 76, folder 2, HI
With the removal of the Russian Front, the conclusion by American planners was the need to shift from the Europe First to Pacific First strategy at the minimum, drawing down forces in the Atlantic purely to those sufficient to safe guard the United Kingdom from a German invasion. With the benefit of hindsight we know this wasn't a realistic concern in terms of invasion, but the JCS was concerned with such given they didn't have access to German documents like we do. In the first document, written by Maj. Gen. Strong, it was recommended negotiations be opened to convene an armistice, as it was not thought possible to defeat the Germans without the Red Army tying down large elements of it.
What about the American public? See
American Popular Opinion and the War Against Germany: The Issue of Negotiated Peace, 1942 by Richard W. Steele,
The Journal of American History , Dec., 1978, Vol. 65, No. 3 (Dec., 1978), pp. 704-723:
The coming of war to America changed but did not destroy the peace issue. Many of those who had stubbornly resisted involvement now hoped to terminate it as quickly as possible, and apparently only a lack of organization significantly differentiated sentiment for a negotiated peace from the isolationism of 1941. Moreover, as the President quickly learned, the leadership for an effective negotiated peace movement seemed likely to emerge from the die-hard remnants of the America First Committee, particularly in the person of the isolationist national hero, Charles A. Lindbergh.
America First officially disbanded in February, and many of its officials announced their support for the war effort. Nevertheless, the activities of some members, including Lindbergh, remained the subject of government interest and concern. In mid-February Federal Bureau of Investigation Director J. Edgar Hoover informed the President that former members of the Committee had "gone underground" and were "biding their time," awaiting the opportunity to emerge again as a "political force." Hoover cited as evidence a mid-December meeting at which the renowned flyer had allegedly held forth on the yellow and Bolshevik menaces, on the foolishness of the current war in Europe, and on what might be done to reverse American policy.
According to Hoover's informant, Lindbergh declared that "when the American people, by reason of the lists of the missing and the statements of war losses, realize that they have been betrayed by the British and the Administration," the Committee should be ready to "advocate a negotiated peace." Hoover also noted that he had obtained information from other sources to the effect that the America Firsters had a "secret mailing list of 8,476,000"; that lately a "great many individuals among foreign speaking groups have been circularized"; and that the leaders of the underground organization planned to hold a "series of house parties . .. to keep alive contacts."34
Further:
Nevertheless, the President could not rest easy, for the fate of the extremists notwithstanding, he had reason to ponder the possibility that his more respectable political enemies might use the peace issue to unsettle and embarrass the administration. In April OFF warned that in the fall congressional campaigns "subversion will probably be intermingled with politics" as both administration opponents and Nazi propagandists seek to "promote defeatism or play upon the war weariness of the people." Fleshing out this prediction was a report informing the President that three leading isolationist Republicans, Congressman Joe Martin, former Congressman Bruce Barton, and publisher Roy Howard, had "just held a secret meeting in far off Tucson," leading to speculation that they were planning an "isolationist attack" against administration war policies. A more explicit warning came to Roosevelt from a friend, New Dealer Gardiner Jackson, who told him in the fall of 1942 that the business interests behind the presidential candidacy of Thomas E. Dewey were working hard for a negotiated peace and had taken a recent conciliatory speech by Hitler as the "opening gun of the drive to call the war off. . . ." The problem raised by these reports (if true) was, as OFF warned, that even if the agitation of the peace issue could not force the administration into negotiations, it could do "much damage" by strengthening "the hand of those in Congress whose main goal is the harassment and obstruction of the President."37